Structural members are available in a wide variety of configurations to provide structural support under a variety of loading conditions. For example, the wing and empennage surfaces of an aircraft typically include parallel and span-wise oriented structural members called stringers that impart flexural stiffness to the wing and empennage surfaces. Typically, a structural member is fabricated from a metal, such as aluminum, steel or titanium, and is configured to resist flexural and/or shear loads. Accordingly, the structural member includes a web portion that is generally planar and oriented in a direction approximately parallel to the applied load so that the web portion offers resistance to a bending moment generated by the load. A flange portion may be positioned on one or both of the longitudinal edges of the web portion in order to provide resistance to localized failure of the web portion due to lateral buckling. The flange portion further allows the structural member to be incorporated into a structure by providing an attachment and/or supporting surface for other adjacent members comprising the structure.
Although the web portion may be planar, other configurations are possible. For example, in one known configuration, a structural member includes a web portion having a generally sinusoidal cross-sectional shape that is positioned between a pair of flanges. The sinusoidal cross-sectional shape is typically formed by moving a planar material through a suitable pair of forming rolls that are configured to impart a sinusoidal cross-sectional shape to the planar material. The web portion may then be cut to a desired length and joined to the flange portions by welding respective edges of the web portion to the flange portions.
One drawback associated with the foregoing structural member is that the welding process that joins the sinusoidal web portion to the flanges typically generates a relatively small fillet radius. Accordingly, structural members formed in this manner exhibit reduced bending and shear resistance due to the small fillet radius. In addition, residual stresses may be introduced into the structural member by the cold-forming process used to form the web portion, and through the welding process used to join the web portion to the flange portions. The residual stresses are typically relieved by subjecting the structural member to a thermal heat treatment process, which generally adds to the fabrication cost of the structural member.
Another possible drawback of the foregoing structural member is that it may be relatively difficult to form attachments, such as mounting brackets, for example, to the sinusoidal-shaped web portion. Although planar surfaces, such as doublers, may be attached to the web portion, the planar surfaces undesirably add weight to the structural member, and require additional forming and joining processes to implement, thus incurring additional fabrication costs. Further, it is often desirable to provide penetrations that extend through the web portion so that other hard ware such as plumbing, electrical wiring, control cables and the like may pass through the structural member. Such penetrations are typically difficult to form in the sinusoidal-shaped web portion. Therefore, structural members that at least partially mitigate these possible disadvantages would have utility.